Direct positive silver halide emulsion

ABSTRACT

A direct positive silver halide emulsion containing at least one dimethinecyanine dye wherein the 3-position of a pyrrolo(2,3 b)pyridine nucleus is bonded through a dimethine chain to the 1-, 2-, 3- or 4-position of a cyanine hetero ring nucleus, provided that where the bonding is in the 4-position the cyanine nucleus is a quinoline nucleus or a pyridine nucleus and where the bonding is in the 1- or 3-position the cyanine nucleus is an isoquinoline nucleus.

Unite States Patent 1 91 1111 3,

Sato et al. Dec. 9, 1975 [54] DIRECT POSITIVE SHJVER HALIDE 3,767,65110/1973 Chapman .1 96/101 EMULSION 3,832,184 8/1974 Sato et a1. 96/101Inventors: Akira Sato; Akira Ogawa; Keisuke Shiba; Masanao Hinato, allof Kanagawa, Japan Fuji Photo Film Co., Ltd., Minami-Ashigara, JapanFiled: Dec. 19, 1973 Appl. No.: 426,145

Assignee:

Foreign Application Priority Data Dec. 19, 1972 Japan 47-127574 US. Cl.96/101; 96/107; 96/108; 96/130; 96/131; 260/240 E Int. Cl. G03C 1/28;G03C l/16 Field of Search 96/107, 108, 130, 131, 96/101; 260/240 EReferences Cited UNITED STATES PATENTS 8/1971 Mee et a1 96/107 PrimaryExaminerW0n H. Louie, Jr. Attorney, Agent, or FirmSughrue, Rothwell,Mion, Zinn & Macpeak [57] ABSTRACT 14 Claims, No Drawings DIRECTPOSITIVE SILVER HALIDE EMULSION BACKGROUND OF THE INVENTION 1. FIELD OFTHE INVENTION The present invention relates to a silver halide emulsionand, more particularly, it relates to a direct positive silver halideemulsion sensitized with a novel dimethinecyanine dye.

2. DESCRIPTION OF THE PRIOR ART When a silver halide light-sensitivematerial is exposed to light of wave-lengths to which the lightsensitive material is sensitive and is development-processed, theresulting photographic density increases as the exposure amountincreases and, ultimately, the photographic density reaches a maximumvalue. However, when the exposure amount is further increased, thephotographic density again is reduced. This phenomenon is generallycalled solarization. Also, with a silver halide lightsensitive materialwhich has been fogged in an optical or chemical manner in the productionof the silver halide emulsion, the same reversal phenomenon (thephenomenon in which the photographic density is reduced with theincrease in the exposure amount) as in the case with light is observed.Positive images can be obtained by utilizing the above-describedphenomenon.

The term direct positive silver halide emulsion as used herein in theinvention means a silver halide emulsion prepared so that a positiveimage can be formed by the usual exposure through a positive originalusing light followed by development processing.

As sensitizers for conventional negative emulsions, many dyes such asmonomethinecyanines, trimethinecyanines, merocyanines, rhodacyanines,and the like are known. However, when these dyes are applied to thesensitization of a direct positive silver halide emulsion, in manycases, a number of defects results, for example, the characteristiccurve becomes non contrasty (or becomes flat) and a re-reversalphenomenon (i.e., a reincrease in the photographic density after thereduction thereof with an increase in the exposure amount) occurs.

In addition, those dyes which have so far been known as sensitizers fordirect positive light-sensitive silver halide emulsions have the defectthat some of the dye remains (hereinafter remaining of the dye or dyeremaining) in the lightsensitive material after processing. Suchremaining of dye is inconvenient particularly with photographic papers.Because, when such dyes are used as the sensitizer, a high whitenesscannot be obtained with a black-and-white photographic paper and, with acolor photographic paper, true color reproduction becomes impossible.Furthermore, such remaining of the dye is even more inconvenient with aconstrasty light-sensitive material, for a copying lithographic typefilm, an X-ray film, a film for copying microphotographs, and the like.

Dyes which are used for sensitizing direct positive emulsions must notpossess any of the abovedescribed defects and must not reduce themaximum density of the image.

SUMMARY OF THE INVENTION It is, therefore, an object of the presentinvention to provide a direct positive silver halide emulsion whichprovides a high sensitivity, which maintains definite maximum imagedensity and which does not cause a substantial remaining of dye.

As a result of extensive investigations to attain the above-describedobjects, the inventors have achieved the present invention. That is, thepresent invention provides a direct positive silver halide emulsioncontaining at least one dimethinecyanine dye wherein the 3position of apyrrolo[2,3-b]pyridine nucleus is connected to the l-, 2-, 3- or4-position of a cyanine hetero ring nucleus (provided that when the4-position is the bonding position, the cyanine nucleus is a quinolineor a pyridine and when the 1- or 3-position is the bonding position thecyanine nucleus is an isoquinoline) through a dimethine chain, andcontaining, if desired, an organic desensitizer.

DETAILED DESCRIPTION OF THE INVENTION Specific examples of thesubstituent at 2-position of the pyrrolo[2,3b]pyridine nucleus of thedimethinecyanine dye which is used in the present invention include alower alkyl group (e.g., having 1 to 4 carbon atoms such as a methylgroup, an ethyl group, a butyl group, etc.), an aryl group (e.g., aphenyl group, etc.). A haloaryl group (e.g., a p-chlorophenyl group,etc.), and a lower alkyl substituted aryl group (e.g., tolyl, etc.).

Specific examples of the cyanine hetero ring nucleus of thedimethinecyanine dye which is used in the invention are, e.g., anoxazoline nucleus, an oxazole nucleus, 21 benzoxazole nucleus, anaphthoxazole nucleus, a thiazoline nucleus, a thiazole nucleus, abenzothiazole nucleus, a naphthothiazole nucleus, a selenazole nucleus,a benzoselenazole nucleus, a naphthoselenazole nucleus, a Z-pyridinenucleus, a 2-quinoline nucleus, a 4- quinoline nucleus a benzoimadazolenucleus, an indolenine nucleus, a 3,3-dialkylindolenine nucleus, animidazo[4,5b]quinoxaline nucleus, a pyrrolindine nucleus, etc. Thesehetero rings and/or benzene nucleusfused hetero rings can obtainedsubstituents. Suitable such substituents are, for example, an alkylgroup (e.g., a lower alkyl group such as a methyl group, an ethyl group,a propyl group, a butyl group), an aryl group e.g., a loweralkylsubstituted aryl group (e.g., a tolyl group, etc.), ahalogensubstituted aryl group (e.g., a pchlorophenyl group, etc.) ahydroxyl group, an alkoxy group (e. g., a lower alkoxy group such as amethoxy group and an ethoxy group), a carboxy group, an alkoxycarbonylgroup (e.g., a lower alkoxycarbonyl group such as a methoxycarbonylgroup and an ethoxycarbonyl group), a nitro group, a halogen atom (e.g.,a chlorine atom, a bromine atom, a fluorine atom, an iodine atom), andthe like.

Specific examples of these cyanine rings are as follows: thiazolesincluding thiazole, 4-methylthiazole, 4- phenylthiazole,4-(p-hydroxyphenyl)-thiazole, 5- methylthiazole, 5-phenylthiazole,4,5-dimethylthiazole, 4,5diphenylthiazole, and the like; benzothiazolesincluding benzothiazole, S-hydroxybenzothiazole, 5-

fluorobmzothiazole, 4-chlorobenzothiazole, 5 chlorobenzothiazole,6-chlorobenzothiazole, 7- chloroben zothiazole, 7-methylben zothiazole,5 methylbenzothiazole, 6-methylbenzothiazole, 5 ,6-

dimethylbenzothiazole, 5-bromobenzothiazole,- 6- bromobenzothiazole,S-phenylbenzothiazole, o-phenylbenzothiazole, 7phenylbenzothiazole,4-methoxybenzothiazole, S-methoxybenzothiazole, 6-methoxybenzothiazole,7-methoxybenzothiazole, 5iodobenzo thiazole, 6-iodobenzothiazole,5-ethoxybenzothiazole, 6-ethoxybenzothiazole,5-ethoxycarbonylbenzothiazole, tetrahydrobenzothiazole,thylarnido)benzothiazole, thiazole, -hydroxybenzothiazole,6-hydroxybenzothiazole, S-nitrobenzothiazole, o-nitrobenzothiazole,5-chloro-6-nitrobenzothiazole, and the like; naphthothiazoles includinga-naphthothiazole, B-naphthothiazole, [3,B-naphthothiazole,5-methoxy-B-naphtho thiazole, 5-ethoxy-B-naphthothiazole,7-ethoxy-oznaphthothiazole, 5-hydroxy-Bnaphthothiazole, 5-ethyl-B-naphthothiazole, and the like; oxazoles including oxazole,4-methyloxazole, 5-methyloxazole, 4- phenyloxazole, 4,5-diphenyloxazole,4-ethyloxazole, 4,5-dimethyloxazo1e, S-phenyloxazole, and the like;benzoxazoles including benzoxazole, 5-chlorobenzoxazole,S-methylbenzoxazole, 5-phenylbenzoxazole, 6- methylbenzoxazole,6-nitrobenzoxazole, 5,6-dimethyl- 5-(N,N-dime- 5,o-dimethoxybenzobenzoxazole, 5-methoxycarbonylbenzoxazole, 5-methoxybenzoxazole, 5-ethoxybenzoxazole, 5- chlorobenzoxazole,S-methoxybenzoxazole, 5 -trilike; l-isoquinolines includingisoquinoline, 3- methylisoquinoline, 4-methylisoquinoline, 7-methylisoquinoline, 8-ethy1isoquinoline, 6-

chloroisoquinoline, 6-methoxyisoquinoline, 8methox yisoquinoline, andthe like; 3-isoquinolines including isoquinoline, S-methylisoquinoline,l-methylisoquinoline, 6-chloroisoquinoline, 6-methoxyisoquinoline, 8-methoxyisoquinoline, and the like; indolenines including indolenine,3,3-dimethylindolenine, 5-hydroxy-3,3- dimethylindolenine,3,3-dimethy1-6-chloroindolenine, 3,3,S-trimethylindolenine,3,3-dimethyl-S-nitroindolenine, and the like; 2-pyridines includingpyridine, 4- butylpyridine, 4-decylpyridine, 4-octadecylpyridine,4,6-dibutylpyridine, 4-benzylpyridine, 4-phenylpyridine,4,6-diphenylpyridine, 4,6-dinaphthylpyridine, 4- chloropyridine,4-bromopyridine, 4,6-dich1oropyri- 6-nitroimidazo4,5-bquinoxaline, 1,3-diphenylimidazo[4,5b]quinoxaline, 6-chlorol ,3-diphenylimidazo4,5-b-quinoxaline, 1,3-diallylimidazo[4,5b]quinoxaline,1,3-dicyclohexylimidazo[4,5b-quinoxaline, and the like; andbenzimidazoles including l-ethylbenzimidazole, l-ethyl-S-nitrobenzoimidazole, l-ethyl-5,6-dichlorobenzimidazole, and the like.

The above-illustrated dimethinecyanine dyes which is used in the presentinvention can be synthesized by reacting under heating apyrrolo[2,3b]pyridine compound aldehyde derivative at 3-positi0n with analkylsubstituted quaternary ammonium salt of a desired cyanine heteroring nucleus-containing compound using a molar ratio of about 1:1 in achemically inert solvent such as acetic acid anhydride, alcohols (e.g.,ethanol, isopropanol, butanol, etc.), nitrobenzene, dimethylformamide,acetonitril, pyridine and morpholine. The solution preferably has aconcentration of from about 0.2 to about 1 mol/l. Where acetic acidanhydride is employed as the solvent, it is preferred that the reactionbe performed at about 150C for about 10 minutes and where ethanol isused as the solvent, it is preferred that the reaction be performed atabout C for about 10 minutes. Basic catalysts such as basicnitrogen-containing organic compounds (e.g., pyperidine, morpholine,triethylamine, etc.) with pyperidine being preferred. However, it is notnecessary to use such a catalyst where acetic acid anhydride is used,since the solvent also functions as a catalyst.

Preferable dimethinecyanine dyes which can be used in the presentinvention can be represented by the following general formula (I);

wherein R represents a hydrogen atom or a lower alkyl group having 1 to3 carbon atoms, R represents a hydrogen atom, a lower alkyl group having1 to 4 carbon atoms or an aryl group, R represents an alkyl group having1 to 6 carbon atoms, a substituted alkyl group, an allyl group or anaryl group, L, represents a methine group, L represents a substituted orunsubstituted methine group (the substituent of L and R can be connectedto each other to form a methylene chain), m and n each represents 1 or2, X- represents an anion, and Z represents the non-metallic atomsnecessary to complete a cyanine hetero ring nucleus.

R and Z in the general formula (I) above have al ready been described indetail before.

Specific examples of suitable alkyl groups for R and 3) R include, e.g.,a methyl group, an ethyl group, a propyl group, a butyl group, etc., andthis alkyl group can E further be substituted with a substituent.Preferred alkyl groups for'R and R are a methyl group or an ethyl group.Specific examples of alkyl groups having 1 to 6 carbon atoms for R are,for example, a methyl group, an ethyl group, a propyl group, a hexylgroup, a 10 hydroxyalkyl group (e.g., a B-hydroxyethyl group, 1 CHZOHetc.), an alkoxyalkyl group (e.g., a B-methoxyethyl max 3 93mm group,etc.), a carboxyalkyl group (e.g., a B-carboxypropyl group, etc.), asulfoalkyl group (e.g., a y-sulfo* propyl group, etc.), an aralkyl group(e.g., a phenethyl group, a benzyl group, etc.), and the like.Particularly (l4) preferable examples of the aryl group for R are, e.g.,a phenyl group, a tolyl group, a p-chlorophenyl group and the like. Rpreferably is a methyl group, an ethyl group or a sulfoalkyl group(e.g., a sulfopropyl group). Specific examples of L include a methinegroup substituted with, e.g., a lower alkoxyalkyl group (e.g., amethoxyethyl group, a ethoxyethyl group, etc.). This-substituent can beconnected to R to form a methylene CH OH chain. In this case, 5- or6-membered ring formation is particularly preferable.

Specific examples of X are, for example, a chloride ion, a bromide ion,an iodide ion, a p-toluenesulfonate ion, an ethylsulfonate ion, aperchlorate ion, etc. n represents I when the compound represented bythe general formula (I) has a betainelike structure and represents 2 inother cases.

Severalspecific examples of the compound represented by the aforesaidgeneral formula (I) are illustrated below together with the data for theabsorption maximum wave-length (A in a methanol solution.

G) N I l z s z s CH CH OH A 461mm CHQOH k 168mm 63 '1 cu -cu -cu-cu,

A CHaOH Lfllnm max C11=CH (1s) I I N N N I l CzHs A CHaOH 14 mm max (19)CH=CH- I I \N 1;!

I cansso H cmon A max Elnm t e on,

N N I CH; H

cn on A max 447mm Examples of the synthesis of the compounds which areused in this invention are described below. Unless otherwise indicatedall parts, percents, ratios and the like given hereinafter are byweight.

SYNTHESIS EXAMPLE 1 Synthesis of Dye (1):

ml of acetic anhydride was added to a mixture of 0.8 g of1-methyl-2-ethyl-3-formylpyrrolo2,3bpyridine and 1.3g ofZ-methyl-l-ethylbenzothiazolium iodide and refluxed for about 10 minutesto react. Then, the reaction mixture was cooled with ice-water and thecrystal precipitated was collected by filtration. The thus obtainedcrystal was recrystallized from a methanol-chloroform mixed solvent toobtain 0.6g of dye (l) (m.p.:256C).

SYNTHESIS EXAMPLE 2 Synthesis of Dye (8):

20ml of acetic anhydride was added to a mixture of 4g ofl-methyl-2-ethyl3-formylpyrrolo[2,3b]pyridine and 9g of2-methyl-1.3diethylimidazo-4,5-b-quinoxalinium p-toluenesulfonatc andrefluxed for about 10 minutes to react. After cooling, the dye wasprecipitated with the diethylether and crystallized by adding thereto asodium iodide aqueous Solution and collected by filtration. The thusobtained crystals were recrystallized from a methanol-chloroform mixedsolvent to ob-. tain 1.6g of dye (8) (mp: 263C).

Other dimethinecyanine dyes can be synthesized according to theabove-described synthesis methods.

It is much more preferable to further incorporate an organicdesensitizier in the direct positive emulsion of the present invention.

The organic desensitizer which can be used in the invention is asubstance which is capable of capturing free electrons generated in thesilver halide grains upon irradiation with radiation and which isadsorbed on the silver halide grains. Further, the organic desensitizeris defined as a Substance having a minimum vacant electron energy levelwhich is lower than the electron energy level of the conduction band ofthe silver halide grains. Preferable desensitizers are compounds havinga maximum occupied electron energy level which is lower than the valenceelectron band of the silver halide grains. The electron energy level ofthe desensitizer can be measured through complicated procedures arerequired.

For example. specific examples of determination on extremely symmetriccyanine dyes are given in Tani and Kikuchi; Photographic Science andEngineering, vol. 1 1 (3), p. 129 (1967), and the specific examples ofdetermination on typical merocyanine dyes are given in Shiba andKubodera; Pre-prinl (N0. B-l2), International Congress of PhotographicScience, 1970 (Moscow). It is known that the electron energy level ofthese compounds is linearly related to both the anode polarographichalf-wave potential (E01) and the cathode polarographic half-wavepotential (B Many of such organic densensitizers are described in, e.g..U.S. Pat. Nos. 3,023,102; 3,314,796; 2,901,351; 3,367,779; British Pat.Nos. 723,019; 698,575; 698,576; 834,839; 667,206; 748,681; 796,873;875,887; 905,237; 907,367; 940,152; French Pat. Nos. 1,520,824;1,518,094; 1,518,095; 1,520,819; 1,520,823; 1,520,821; 1,523,626;Belgian Pat. Nos. 722,457; 722,594; Japanese Pat. Publication Nos.13167/68; 14500/68; and the like.

As the organic desensitizers which can be used in the invention, any ofthose as described above can be employed. However, particularlypreferable results can be provided by compounds which have a cathodepolarographic half-wave potential (E more positive'than -l .0 volt andare represented by the following general formula (III);

x (III) wherein Z, X and m are the same as defined in the generalformula (I), R represents an alkyl group or an allyl group (eg, havingfrom 1 to 8 carbon atoms, pref erably l to 4 carbon atoms), and arepresents 1 or 2.

Specific examples of R include a methyl group, an ethylgroup, a butylgroup, a hydroxyalkyl group (e.g., a hydroxyethyl group, etc. acarboxyalkyl group (e.g., a carboxymethyl group, a 3-carboxypropylgroup, etc.), a sulfoalkyl group (e.g., a 2-sulfoethyl group, a4-sulfobutyl group, etc), and the like.

Specific organic desensitizers which can be used in the invention are,e.g., phenosafranine, pinakryptol yellow, -m-nitrobenzylidenerhodanine,3-ethyl-5-mnitrobenzylidenerhodanine,3-ethyl-5-(2,4-dinitrobenzylidene)rhodanine,5-o-nitrobenzylidene3-phenylr hodanine,1,3-diethyl-6-nitrothia-2-cyanine iodide, 4-nitro-6-chlorobenzotriazole,3,3-diethyl-6,6'-dinitro-9-phenylthiacarbocyanine iodide,2-(p-dimethylaminophenyliminomethyl) benzothiazole ethoeth' ylsulfate,Crystal Violet, 3,3 -diethyl-6,6-dinitrothiacarbocyanine ethylsulfate, 1,3-diethyl-6-nitrothia2 cyanine iodide, 1,3-diamin-5-methylphenaziniumchloride, 4-nitro-6chlorobenzotriazole,3,3-di-p-nitrobenzylthiacarbocyanine bromide, 3,3-di-p-nitrophenylthiacarbocyanine iodide,3,3-dionitrophenylthiacarbocyanine perchlorate,3,3'-dimethyl-9-trifluoromethylthiacarbocyanine iodide, 9-(2,4-dinitrophenylmercapto 3 ,3 -diethylthiacarbocyanine iodide,bis(4,6-diphenylpyrryl-2-trimethinecyanine perchlorate, anhydrousZ-p-dimethylaminophenyliminomethyl-6-nitro-3-(4-sulfobutyl)-benzothiazoliumhydroxide, l-(2benzothiazolyl)-2-(p-dimethylaminostyryl)-4,6-diphenylpyridiniumiodide, 1,3- diethyl-5l ,3-neopentylene-6-( 1 ,3,3-trimethyl-2-indolynilidene)-2,4-hexadienylidene-2-thiobarbituric acid,2,3,5-triphenyl-ZH-tetrazolium chloride, 2-(4-iodophenyl)-3-(4-nitrophenyl)-5-phenyl-tetrazolium chloride,l-methyl-8-nitroquinolinium methylsulfate,3,6-bis-4-(3-ethyl-2-benzothiazo1ynilidene)-2-butenylidene-l,2.4,5-cyclohexanetetrone, and the like.

As the silver halide emulsions which can be used in the invention, thereare, e.g., a silver chloride emulsion, a silver bromide emulsion, asilver chlorobromide emulsion, a silver chloroiodide emulsion, silveriodobromide emulsion, silver chloroiodide emulsion, and the like, asdisclosed in U.S. Pat. Nos. 2,401,051; 2,717,833; 2,976,149; 3,023,102;3,501,306; 3,501,307; 3,501,310 and 3,531,288.

The size of the silver halide grains in these emulsions can be withinthe range usually employed. However, when the mean grain size is 0.05;;to 1.0a, preferably 0.2 to 1 a, particularly advantageous results can beobtained. Also, the silver halide grains which can be used in theinvention can be either regular grains or irregular grains, though theformer provides better effects in the present invention.

Either monodispersed emulsion or mon-monodispersed emulsion can be usedin the present invention, although the former is more preferable.

In general, original emulsions which can be used for the direct positivesilver halide light-sensitive material are classified into the followingtwo groups.

One group of light-sensitive materials are those which have, in theinside of the silver halide crystal, nuclei capable of trapping freeelectrons, the surface of the silver halide having previously beenchemically fogged. This type of emulsion is characterized by the abilityper se to provide a positive image directly. They can be made highlysensitive due to spectral sensitization through the addition of asensitizing dye and, in ad dition, the sensitivity in the intrinsicabsorption region can be increased. With this type of emulsion, thesilver composition must be formulated so that the chemical sensitizerand the salt of Group VIII metal which is used for imparting freeelectrontrapping nuclei can be absorbed inside the silver halide grains.By the addition of the organic desensitizer, clearing property can beimproved and, in particular, re-reversal can be pre vented. Also, by theaddition of bromide ions and iodide ions, the maximum density andsensitivity can be increased and the clearing property can be improved.

Another type of light-sensitive materials for the original emulsions arethose which are not provided with free electrontrapping nuclei insidethe silver halide grains, the surface of the grains having beenchemically fogged. This type of emulsion contains as little latticedefects as is possible and, preferably comprises pure silver bromideregular crystals having no twin plane. This type of emulsion itselfprovides no direct positive image. However, when an organic desensitizeris adsorbed on the silver halide grains of this emulsion, a directpositive image can be obtained with high sensitiv ity.

In the present invention, either type of emulsions can be used. In otherwords, either type of original emulsion can effectively be sensitized bythe compound represented by the general formula (I). These emulsions arewell known and examples thereof are disclosed in U.S. Pat. Nos.2,401,051; 2,717,833; 3,976,149; 3,023,102; 3,501,306; 3,501,306;3,501,307; 3,501,310 and 3,531,288.

The silver halide emulsions which can be used in the invention arefogged optically or chemically as disclosed in U.S. Pat. Nos. 2,497,875;2,588,982; 3,023,102; and 3,367,778. Chemical fogging nuclei areprovided by adding a reducing organic compound such as hydrazinederivative, formaldehyde thiourea dioxide, a polyamine compound, anamineborane, methyldichlorosilane or the like. In addition, a method ofimparting fogging nuclei by the combined use of the reducing agent andan ion of metal more noble than silver (e.g., a gold ion, a platinumion, an iridium ion, etc.) or, further, a halogen ion can be ap'plied.

In the emulsion which can be used in the present invention, gelatin ismainly used as the protective colloid. Inert gelatin is particularlyadvantageous. In addition, in place of gelatin, photographically inertgelatin derivatives (e.g., phthaloylated gelatin, etc.), watersolublesynthetic polymers (e.g., polyvinyl acrylate, polyvinylalcohol,polyvinylpyrrolidone, polyvinylalginic acid, carboxymethyl cellulose,hydroxymethyl cellulose, etc.), or the like can also be used. i

In the direct positive silver halide emulsion of the present invention afogging nuclei-stabilizing agent (e.g., a mercapto compound, a thionecompound, tetrazaindene compound. etc. as disclosed in U.S. Pat. Nos.2,444,605; 2.444,606; 2.444,607 and 2,444,608), a clearingproperty-improving agent (e.g., a stylbene compound, a triazinecompound, etc. as disclosed in U.S. Pat. No. 3,023,102), a brighteningagent (as dis closed in U.S. Pat. No. 3,406,070), an ultravioletabsorbant (as disclosed in U.S. Pat, No. 3,434,837), a hardening agentchromium alum, a 2,4dichloro' S-triazine compound, an aziridinecompound, an epoxy compound, a mucohalogenic acid (a halogen formylmaleic acid compound as disclosed in US. Pat. Nos. 3,288,775; 3,017,280and 2,983,611)), a coating aid (e.g., sodium polyalkylenesulfonate,saponin, an anionic surface active agent having a betaine structure,etc. as disclosed in US. Pat. Nos. 3,068,101; 3,415,649 and 2,600,831),an antiseptic as disclosed in British Pat. No. 987,010, a plasticizer(e.g., a polyalkyl acrylate, a copolymer of alkyl acrylate and acrylicacid, or a like vinyl polymer, a polyalkylene oxide, etc.), a colorcoupler as disclosed in US. Pat. Nos. 2,376,679; 2,698,794; 3,046,129and 3,227,554, or like additives can be incorporated.

The amount of the dimethine dye which can be used in the inventioncannot be set forth specifically since the amount varies depending uponthe amount of silver halide in the emulsion and the surface area of thesilver halide grains. However, an amount of about 1 X 10 to 2 X 10 molper 1 mol of silver salt provides particularly preferable results. Thesedyes are used by dissolving in water or a water-miscible solvent such asmethanol, ethanol, ethylene glycol monomethyl ether, methyl ethylketone, acetone, pyridine, and' the like. Ultrasonic vibration can beused for the dissolution of these dyes. Also, methods employed uponsensitizing negative-type emulsions described in, e.g., US. Pat. Nos.3,482,981; 3,585,195; 3,469,987; 3,649,286; 3,485,634; 3,342,605 and2,912,343, etc. can be used.

The addition of the dyes to an emulsion is conveniently conductedimmediately before coating. However, the dyes can be added duringchemical ripening or upon formation of the silver halide.

The amount of the organic desensitizer which can be used in theinvention cannot be set forth specifically since it also variesdepending upon the kind of the desensitizer used. However, thedesensitizer is added preferably in an amount of about 2 X l to 10 molper 1 mol of the silver halide.

The emulsion in accordance with the present invention can be applied tovarious supports to prepare photographic elements. Preferably thethickness ranges from about to p The emulsion can be applied to the oneside or both sides of the support, which can be either transparent oropaque. Representative examples of supports include a cellulose nitratefilm, a cellulose acetate film, a polyvinyl acetal film, a polystyrenefilm, a polyethylene terephthalate film, and other polyester films,glass, metal, wood, etc. In addition, a support prepared by laminatingpaper with a plastic can also be used,

The emulsion of the present invention can be suitably processed, afterexposure, using the conventionally known processing baths fordevelopment, fixation, stabilization, or using a combined processingbath.

A first feature of the present invention is the sensitization of adirect positive silver halide emulsion with a novel dimethine dye havinga pyrrolo-2,3-b-pyridine nucleus, which substantially does not cause anyremaining of dye.

US. Pat. No. 2,323,187 describes that a large amount of sensitizing dyehaving sensitizing action on conventional negative emulsions,particularly a carbocyanine dye, is effective for the sensitization ofdirect positive emulsions. However, this method is not preferred sincethe dye strongly colors the emulsion and results in the dye remaining.On the otherhand, British Pat. Nos. 970.621 and 1,186,714 describe thatdimethine dyes having a 2phenylindole nucleus or a 2 pyridylindolenucleus shows excellent reversal property. However, even such dyes arenot satisfactory due to the dye remaining. In addition, when such dyesare added to the direct positive emulsion to the extent that maximumsensitivity is provided, the tendency of the dye to remain becomesparticularly great.

The dimethine dyes having a pyrrolo[2,3b]pyridine nucleus of the presentinvention are characterized in that the remaining of the dye is markedlyreduced.

A second feature of the present invention is that the maximum density ofthe direct positive emulsion is not substantially lowered.

In many cases, dimethine dyes having a 2-phenylindole nucleus, as wellas carbocyanine dyes and merocyanine dyes useful for thesensitization ofconventional negative emulsions, reduce the maximum density of thedirect positive emulsion. The reduction in maximum density occurs duringstorage with the passage of time as well as immediately after coatingthe direct positive emulsion. This deterioration of the direct positivephotographic light-sensitive material with the passage of time tends tobe greater than the deterioration in conventional negativelight-sensitive materials. Therefore, removal of this defect has been ofgreat concern. The novel dimethine dye which is used in the presentinvention shows excellent characteristics in this respect, also.

A third feature of the present invention is that the dimethine dyeswhich are used in the present invention result in less remaining of thedye and the characteristic curve is not so flat (non-contrasty). Ingeneral, a carbocyanine dye or a merocyanine dye useful for thesensitization of a negative emulsion has a strong tendency to have aflatened characteristic curve. This phenomenon of the characteristiccurve becoming flat is not preferable for a contrasty direct positivelight-sensitive material such as a film for a copying lithographictypefilm.

Also, the direct positive silver halide emulsion sensitized with thedimethine dye of the invention has the feature that'the clearingproperty (minimum density) is good and rereversal phenomenonsubstantially is not caused. I

The novel dimethine dye which is used in the present invention has theexcellent characteristicsas described above. The reversal sensitivitycan be enhanced even more by the combined ,use of the dye and an organicdesensitizer. This combined use enables the production of a directpositive silver halide emulsion having a good clearing property.

The direct positive silver halide emulsion of the present invention canbe used for contrasty direct positive .silver halide light-sensitivematerials such as a light-sensitive material for copying lithographictype films, a light-sensitive material for duplicating original drawingsand, in addition, for comparatively non-contrasty direct positive silverhalide light-sensitive materials such as a light-sensitive material forcopying microphotographis, and a light-sensitive material for copyingX-ray photographs. In addition, it can be used for color light-sensitivematerials.

The direct positive silver halide emulsion in accordance with thepresent invention can be exposed using the irradiation of electronbeams, X-rays, gamma-rays, etc. as well as the irradiation with light.

The present invention will now be illustrated in greater detail byreference to the following non-limiting examples of preferredembodiments of the invention. Additionally, the dye used for comparisonin the examples was the following compound. (A)

EXAMPLE 1 First, in order to prepare an original emulsion, Solutions 1 4having the following formulations were prepared.

Solution 1 lnert Gelatin 8 g An aqueous Solution of Potassium cc Bromide(1 N) Water (60C) 500 cc Solution 2 Silver Nitrate 100 g Water (60C) 500cc Solution 3 Potassium Bromide 70 g Water (60C) 150 cc Solution 4 lnertGelatin 75 g Water 300 cc Solution 2 and Solution 3 were added toSolution 1 over a 50 minute period while maintaining the temperature at60C and then subjected to physical ripening for 5 minutes. Then, 15cc ofa 0.2 N potassium iodide solution was added thereto and the pAg wasadjusted to 6.0 using a silver nitrate solution. The pH of the solutionwas adjusted to using a sodium hydroxide aqueous solution. Then,hydrazine (0.005 millimole per mole of silver halide) and gold chloride(0.005 millimole per mole of silver halide) were added thereto and theripening was conducted for 10 minutes. After neutralizing with citricacid, the emulsion was washed with water. Then, Solution 4 was addedthereto after melting to thereby obtain an original emulsion. The thusobtained emulsion contained regular tetragonal silver halide grains of amean grain size of about 0.2 which have the crystal face of (100). I

To the resulting original emulsion portions were added the dye as setforth and in the amount described in Table l and, further, saponin wasadded (20ml of a 1% solution per kg of emulsion) to the emulsion. Eachof the resulting emulsion portions was applied to a cellulose triacetatefilm in a dry thickness of about 5 microns to obtain samples. Eachsample was wedgewise exposed using a 2854K tungsten light as a lightsource. Then each of them was development-processed at 20C for 2 minutesusing the following developer and fixed in an acidic hardening andfixing solution. The density was measured using a Model P densitometermade by the Fuji Photo Film Co., Ltd. to obtain characteristic curves.The results of sensitivity, maximum optical density (Dmax) and minimumoptical density (Dmin) obtained are shown in Table 1. Additionally, thesensitivity is represented in terms of the reciprocal of the exposureamount necessary for providing a density of Dmax Dmin 16 taking thesensitivity of the dye (A) for comparison as 100.

Composition of the Developer:

Metol 3.1 g Anhydrous Sodium Sulfite 45 g Hydroquinone 12 g SodiumCarbonate Monohydrate 79 g g l Potassium Bromide I 2 Water to make 1Upon use, this composition was diluted 1:1 by volume with water.

From the results contained in Table 1, it can be seen that, as comparedwith the dye for comparison, the dye used in the present invention hassuch excellent properties that it provides a high Dmax, a good clearingproperty and a high sensitivity.

EXAMPLE 2 First, an original emulsion was prepared in the followingmanner. Solution 2 (prepared by adding 500cc of water to 100g of silvernitrate and heating to 60C to dissolve) and Solution 3 (prepared vbyadding 300g of water to 35g of sodium chloride and heating to 60C todissolve) were added to Solution 1 (prepared by adding Sec of a 1 Nsodium chloride solution and 500cc of water to 10g of inert gelatin andheating to 60C to dissolve) over a 20 minute period under stirring whilemaintaining the temperature at 60C. After the completion of theaddition, ripening was conducted for 5 minutes. Then, Solution 4(prepared by adding 200cc of water to 14g of potassium bromide andheating to 60C to dissolve) was added thereto over a 5 minute periodunder stirring. Then, ripening was conducted for 10 minutes and, afterreducing the temperature, the emulsion was washed with water. Then, itwas again heated to dissolve, and the pH was adjusted to 10 followed byadding hydrazine (0.005 millimole per mole of silver halide) and a goldchloride salt (0.005 millimole per mole of silver halide) to ripen for10 minutes. Thereafter, the pH was adjusted to 6.5 using citric acid.Further, Solution 6 (prepared by adding 30000 of water to g of inertgelatin to dissolve) was added thereto to obtain an original emulsion.The thus obtained original emulsion contained silver halide grains of amean grain size of about 0.15 micron.

To the resulting original emulsion portions were added 32cc of amethanol solution of pinakryptol yellow of a molar concentration of 5 X10 and the dye in the amount as set forth in Table 2. Further,mucochloric acid (20ml of a 2% solution per kg of emulsion) and saponin(20ml of a 1% solution per kg of emulsion) were added thereto insuitable amounts. Each of the resulting emulsion portions was applied toa cellulose triacetate film in a dry thickness of about 2 microns toobtain samples.

Each sample was exposed through an optical wedge using as a 2854Ktungsten light as a light source followed by development-processing at20C for 3 minutes with a developer having the following formulation andfixing in an acidic hardening and fixing solution.

Composition of the Developer:

Water (about 30C) 50 cc Anhydrous Sodium Sulfite 30 g Paraformaldehyde7.5 g Sodium Bisulfite 2.2 g Boric Acid 7.5 g Hydroquinone 22.5 gPotassium Bromide 1.6 g

Water to make The density was measured using a Model P densitometer madeby the Fuji Photo Film Co., Ltd. to obtain 1 TABLE 2 Dye (Molar Concen-Density of Samp tration) cc/lg SenSi Remaining No. Emulsion tivity DmaxDmin Dye 9 1(8 X 10 2) 24 H7 30- 0.04 0.0l l0 3 (8 X l0 8 l5l 3.l 0.050.06 ll 4 (8 X 10 32 257 2.9 0.04 0.01 12 7 (8 X 10 8 132 3.0 0.06 0.05l3 l4 (8 X 10 I6 112 3.2 0.04 0.04 l4 l6 (8 X 10) 24 115 2.8 0.04 0.0]15 17(8 X 10 24 151 3.0 0.04 0.01 16 (8 X 10*) 32 228 2.8 0.04 0.01 l7 A(8 X l0" l6 lOO 2.5 0.08 0.08

From the results contained in Table 2, it can be seen that, as comparedwith the dye for comparison, the dye used in the invention showsexcellent sensitivity, maximum optical density and clearing propertyand, in addition, causes less remaining of the dye, when used incombination with the organic desensitizer.

While the invention has been described in detail and with reference tospecific embodiments thereof, it will be apparent to one skilled in theart that various 18 changes and modifications can be made thereinwithout departing from the spirit and scope thereof.

What is claimed is:

1. A direct positive prefogged silver halide emulsion containing atleast one dimethinecyanine dye wherein the 3-position of a pyrrolo[2.3b] pyridine nucleus is bonded through a dimethine chain to the 1-,2-, 3 or 4-position of a cyanine hetero ring nucleus, provided thatwhere the bonding is in the 4-position said cyanine nucleus is aquinoline nucleus or a pyridine nucleus and where the bonding is in thelor 3-position said cyanine nucleus is an isoquinoline nucleus, saiddimethincyanine dye being present in an amount sufficient to sensitizesaid emulsion.

2. The direct positive silver halide emulsion as claimed in claim 1,wherein said emulsion contains an organic desensitizer.

3. The direct positive silver halide emulsion as claimed in claim 1,wherein said cyanine hetero ring nucleus is an oxazoline nucleus, anoxazole nucleus, a benzoxazole nucleus, a naphthoxazole nucleus, athiazoline nucleus, a thiazole nucleus, a benzothiazole nucleus, anaphthiazole nucleus, a selenazole nucleus, a benzoselenazole nucleus, anaphthoselenazole nucleus, a 2-pyridine nucleus, a 2-quinoline nucleus,a 4-quinoline nucleus, a benzoimidazole nucleus, an indolenine nucleus,a 3,3-dialkyindolenine nucleus, an imida- Zo[4,5b]quinoxaline nucleus,or a pyrrolidine nucleus.

4. The direct positive silver halide emulsion as claimed in claim 1,wherein said dimethinecyanine dye is represented by the followinggeneral formula (I);

wherein R represents a hydrogen atom or a lower alkyl group, Rrepresents a hydrogen atom, a lower alkyl group or an aryl group, Rrepresents an alkyl group having 1 to 6 carbon atoms, L represents amethine group, L represents a methine group, wherein said L and R can beconnected to each other to form a methylene chain, In and n eachrepresents 1 or 2, X represents an anion, and Z represents thenon-metallic atoms necessary to complete a cyanine hetero ring nucleus.

5. The direct positive silver halide emulsion as claimed in claim 4,wherein said alkyl group for R, is a methyl group, an ethyl group, or apropyl group; wherein said alkyl group for R is a methyl group, an ethylgroup, or a butyl group wherein said aryl group for R is a phenyl group,a tolyl group or a p-chlorophenyl group; wherein said alkyl group for Ris an alkyl group, a hydroxyalkyl group, an alkoxyalkyl group, acarboxyalkyl group, a sulfoalkyl group, or an aralkyl group; whereinsaid aryl group for R is a phenyl group, a tolyl group or ap-chlorophenyl group; wherein said methine group for said L is a methinegroup or a lower alkoxyalkyl-substituted methine group, said substituentbeing a methoxyethyl group or an ethoxyethyl group and wherein thenon-metallic atoms represented by Z form an oxazoline nucleus, anoxazole nucleus, a benzoxazole nucleus, a naphthoxazole nucleus, athiazoline nucleus, a thiazole nucleus, :1 benzothiazole nucleus, 21

naphthothiazole nucleus, a selenazole nucleus, a benzoselenazolenucleus, a naphthoselenezole nucleus, a 2-pyridine nucleus, aZ-quinoline nucleus, a 4-quinoline nucleus, a benzoimidazole nucleus, anindolenine nucleus, a 3,3-dialkylindolenine nucleus, animidazo[4,5b]quinoxaline nucleus, or a pyrrolidine nucleus. 6. Thedirect positive silver halide emulsion as claimed in claim 3, whereinsaid cyanine hetero ring nucleus is a benzothiazole nucleus, abenzoselenazole nucleus, at benzoxazole nucleus, 3,3-dialkylindoleninenucleus, or an imidazo[4,5b] quinoxaline nucleus.

halide emulsion contains-a photographic color coupler.

1 l. The direct positive silver halide photographic emulsion as claimedin claim 2, containing at least one dye selected from the dyesrepresented by the following general formula (I);

2 (cH-cii) -N-R3 (I) N I (x wherein R represents a hydrogen atom or alower alkyl group, R represents a hydrogen atom, a lower alkyl group oran aryl group, R represents an alkyl group having 1 to 6 carbon atoms,L, represents a methine group, L represents a methine group, whereinsaid L and R can, be connected to each other to form a methylene chain,In and n each represents 1 or 2, X represents an anion, Z represents thenon-metallic atoms necessary to complete a cyanine hetero ring nucleus,and an organic desensitizer represented by the following general formula(Ill); 7

7. The direct positive silver halide emulsion as claimed in claim 1,wherein said silver halide of said emulsion comprises chemically foggedsilver halide grains.

8. The direct positive silver halide emulsion as claimed in claim 7,wherein said silver halide of said emulsion comprises silver halidegrains fogged with a reducing agent and a gold compound.

9. The direct positive silver halide emulsion as claimed in claim 7,wherein at least 95% by weight of said fogged silver halide grains havea diameter within about of the mean grain size of said silver halidegrains.

10. The direct positive silver halide emulsion as claimed in claim I.wherein said direct potitive silver (III) wherein R represents an alkylgroup or an allyl group, X, Z, and m are the same as defined above, anda represents l or 2.

12. A direct positive silver halide light-sensitive material comprisinga support having thereon the direct positive silver halide emulsion asclaimed in claim 1.

13. The direct positive silver halide photographic emulsion as claimedin claim 1 wherein the sensitizing amount is within the range of from lX 10 to 2 X 10 mol of dye per mol of silver halide.

14. The direct positive silver halide lightsensitive material as claimedin claim 12 wherein the sensitizing amount is within the range of from lX 10' to 2 X l0 mol of dye per mol of silver halide.

l l l

1. A DIRECT POSITIVE PREFOGGED SILVER HALIDE EMULSION CONTAINING ATLEAST ONE DIMETHINECYANINE DYE WHEREIN THE 3-POSITION OF A PYRROLO(2,3B) PYRIDINE NUCLEUS IS BONDED THROUGH A DIMETHINE CHAIN TO THE 1-,2-, 3- OR 4-POSITION OF A CYANINE HETERO RING NUCLEUS, PROVIDED THATWHERE THE BONDING IS IN THE 4-POSITION SAID CYANINE NUCLEUS IS AQUINOLINE NUCLEUS OR A PYRIDINE NUCLEUS AND WHERE THE BONDING IS IN THE1- OR 3-POSITION SAID CYANINE NUCLEUS IS AN ISOQUINOLINE NUCLEUS, SAIDDIMETHINCYANINE DYE BEING PRESENT IN AN AMOUNT SUFFICIENT TO SENSITIZESAID EMULSION.
 2. The direct positive silver halide emulsion as claimedin claim 1, wherein said emulsion contains an organic desensitizer. 3.The direct positive silver halide emulsion as claimed in claim 1,wherein said cyanine hetero ring nucleus is an oxazoline nucleus, anoxazole nucleus, a benzoxazole nucleus, a naphthoxazole nucleus, athiazoline nucleus, a thiazole nucleus, a benzothiazole nucleus, anaphthiazole nucleus, a selenazole nucleus, a benzoselenazole nucleus, anaphthoselenazole nucleus, a 2-pyridine nucleus, a 2-quinoline nucleus,a 4-quinoline nucleus, a benzoimidazole nucleus, an indolenine nucleus,a 3,3-dialkyindolenine nucleus, an imidazo(4,5b)quinoxaline nucleus, ora pyrrolidine nucleus.
 4. The direct positive silver halide emulsion asclaimed in claim 1, wherein said dimethinecyanine dye is represented bythe following general formula (I);
 5. The direct positive silver halideemulsion as claimed in claim 4, wherein said alkyl group for R1 is amethyl group, an ethyl group, or a propyl group; wherein said alkylgroup for R2 is a methyl group, an ethyl group, or a butyl group whereinsaid aryl group for R2 is a phenyl group, a tolyl group or ap-chlorophenyl group; wherein said alkyl group for R3 is an alkyl group,a hydroxyalkyl group, an alkoxyalkyl group, a carboxyalkyl group, asulfoalkyl group, or an aralkyl group; wherein said aryl group for R3 isa phenyl group, a tolyl group or a p-chlorophenyl group; wherein saidmethine group for said L2 is a methine group or a loweralkoxyalkyl-substituted methine group, said substituent being amethoxyethyl group or an ethoxyethyl group and wherein the non-metallicatoms represented by Z form an oxazoline nucleus, an oxazole nucleus, abenzoxazole nucleus, a naphthoxazole nucleus, a thiazoline nucleus, athiazole nucleus, a benzothiazole nucleus, a naphthoThiazole nucleus, aselenazole nucleus, a benzoselenazole nucleus, a naphthoselenezolenucleus, a 2-pyridine nucleus, a 2-quinoline nucleus, a 4-quinolinenucleus, a benzoimidazole nucleus, an indolenine nucleus, a3,3-dialkylindolenine nucleus, an imidazo(4,5b)quinoxaline nucleus, or apyrrolidine nucleus.
 6. The direct positive silver halide emulsion asclaimed in claim 3, wherein said cyanine hetero ring nucleus is abenzothiazole nucleus, a benzoselenazole nucleus, a benzoxazole nucleus,3,3-dialkylindolenine nucleus, or an imidazo(4,5b) quinoxaline nucleus.7. The direct positive silver halide emulsion as claimed in claim 1,wherein said silver halide of said emulsion comprises chemically foggedsilver halide grains.
 8. The direct positive silver halide emulsion asclaimed in claim 7, wherein said silver halide of said emulsioncomprises silver halide grains fogged with a reducing agent and a goldcompound.
 9. The direct positive silver halide emulsion as claimed inclaim 7, wherein at least 95% by weight of said fogged silver halidegrains have a diameter within about 40% of the mean grain size of saidsilver halide grains.
 10. The direct positive silver halide emulsion asclaimed in claim 1, wherein said direct potitive silver halide emulsioncontains a photographic color coupler.
 11. The direct positive silverhalide photographic emulsion as claimed in claim 2, containing at leastone dye selected from the dyes represented by the following generalformula (I);
 12. A direct positive silver halide light-sensitivematerial comprising a support having thereon the direct positive silverhalide emulsion as claimed in claim
 1. 13. The direct positive silverhalide photographic emulsion as claimed in claim 1 wherein thesensitizing amount is within the range of from 1 X 10 6 to 2 X 10 2 molof dye per mol of silver halide.
 14. The direct positive silver halidelightsensitive material as claimed in claim 12 wherein the sensitizingamount is within the range of from 1 X 10 6 to 2 X 10 2 mol of dye permol of silver halide.